When overall power demand is low, power producers often turn their power generation equipment to a low power level so as to conserve fuel. In the case of a gas turbine engine, the inlet guide vanes about a compressor inlet may be closed to a minimum angle so as to reduce the airflow therethrough and the overall power output. Specifically, the air passing through the inlet guide vanes may experience a significant pressure drop at the low inlet guide vane angles. The front end of the compressor essentially acts as a turbine and extracts energy from the airflow in a phenomenon called turbining. The low pressure thus may cause the temperature of the airflow about the compressor inlet casing to drop quickly. Such low temperatures may require more steady state clearances between the casing and the rotor blades to allow for stabilization.
Because the metal casing of the compressor has a slower thermal response time than the rotor blades, the rotor blades may expand faster than the casing so as to cause the rotor blades to close in on the casing and potentially rub thereagainst when in transition to higher loads or in an overspeed condition. Rubbing may cause early rotor blade damage and possible failure. As a result, operational rotor blade/casing clearances must accommodate these differing expansion rates. These clearances effect and thereby limit the amount of core flow that may be pulled into the compressor.
There is therefore a desire for improved clearance control systems and methods for a compressor so as to improve overall gas turbine engine performance and efficiency. Preferably, the improved compressor clearance control systems and methods also should address turbining during low or no load conditions as well rotor blade rubbing during load transitions. Specifically, reducing the range of clearances over the operating regime without the danger of not enough clearances (rubbing, damage) or the danger of too much clearance (loss of performance, stall, damage).